In electron microscopy, a specimen is observed while placed in a high vacuum. Therefore, if the specimen is a biological specimen, it dries. This makes it impossible to observe the specimen in the unmodified state. To cope with this situation, an atmospheric pressure specimen-holding device using an environmental cell as shown in FIG. 5 has been developed.
Referring to FIG. 5, the environmental cell, indicated by 2, is placed in a microscope column 1. A specimen 8 in an unmodified state is held in the cell 2. A moist gas is introduced into the cell 2 through an intake port 3. Also, water is admitted into the cell 2 through a water intake port 4. The cell 2 is connected with an exhaust port 5, and the inside of the cell 2 is evacuated by a vacuum pump (not shown). Magnetic pole pieces 9a and 9b of an objective lens 9 are mounted, respectively, above and below the specimen. An electron beam converged by the objective lens 9 is directed to the specimen 8 via sealing films 6 and 7. An image of the specimen is created from electrons transmitted through the specimen 8.
Although the environmental cell 2 is evacuated by the vacuum pump, the inside of the cell is kept permeated with a gaseous ambient containing moisture, because gas and water are supplied into the cell 2. Consequently, the specimen is prevented from drying. Thus, the specimen can be observed in an almost unmodified state.
In the specimen holder shown in FIG. 5, the environmental cell 2 is thick and so the electron beam collides with water molecules and other substances contained in the cell, thus producing a large amount of beam induced ions. The produced ions bombard the specimen and thus damage it. This damage to the specimen is much heavier than the damage that the specimen sustains by electron beam irradiation. Hence, the specimen cannot be observed in its intact state.
In the above-described prior art specimen holder, a system for supplying water into the cell, equipment for evacuating the cell, and a control system for controlling the water supply system and the evacuating equipment are needed. This makes the whole apparatus bulky and complex. Also, the apparatus is not satisfactorily economical to fabricate.
It is an object of the present invention to provide a specimen-holding device which is for use with an electron microscope or the like and which permits a specimen to be observed in an almost unmodified state.
It is another object of the invention to provide a specimen-holding device which is for use with an electron microscope or the like and which permits a specimen to be observed in an almost unmodified state, is relatively simple in structure and is economical to fabricate.
In the present invention, a pair of films transmitting an electron beam are reinforced with a network of reinforcing members. A specimen to be investigated is held between these films. The fringes of the films are seal by O-rings, thus hermetically isolating the space sandwiched between the films. The specimen is observed within an atmosphere where water exists. Since the specimen is merely sandwiched between the films, the atmosphere through which the electron beam passes can be made quite thin. When the beam is made to impinge on the specimen, only a small amount of ions is produced inside the atmosphere. Consequently, the damage to the specimen by ion bombardment is negligibly small.